Render Delegation

Usage

For certain components, we set a default underlying HTML element to wrap the children with. As a high level example, the Accordion.Trigger, looks something like this:

	<button>
	{@render children()}
</button>

While we do allow you to set any attribute that you normally could on a button, let's say you want to apply a Svelte Transition or Svelte Action to the button, or use a custom component you've made, that's when render delegation comes into play.

Each of the components that support render delegation accept an optional prop called child, which is a Snippet. When used, the component will pass the attributes as a snippet prop, which you can then apply to the element of your choosing. Note, if you use child any other children that aren't within that child snippet will be ignored.

Let's take a look at an example using the Accordion.Trigger component:

	<Accordion.Trigger>
	{#snippet child({ props })}
		<div {...props}>Open accordion item</div>
	{/snippet}
</Accordion.Trigger>

We're passing all the props/attribute we would normally apply to th <button> within the component to whatever element we want. These props include event handlers, aria attributes, and any other attributes you passed into the Accordion.Trigger component.

Custom IDs & Attributes

If you wish to use a custom ID, event handlers, or other attributes with a custom element, you must pass them to the component first. A lot of Bits UI internals rely on the ID, and these props are merged via mergeProps so you'll need to do something like this:

	<Accordion.Trigger id="my-custom-id" onclick={() => console.log("clicked")}>
	<!-- your custom ID and event handler is now inside the `props` object -->
	{#snippet child({ props })}
		<div {...props}>Open accordion item</div>
	{/snippet}
</Accordion.Trigger>

Behind the scenes this is what's happening (pseudo):

	<script lang="ts">
	// other imports/props/logic omitted for brevity
	let { child, children, ...restProps } = $props();
	const trigger = makeTrigger();
 
	const mergedProps = $derived(mergeProps(restProps, trigger.props));
</script>
 
{#if child}
	{@render child({ props: mergedProps })}
{:else}
	<button {...mergedProps}>
		{@render children?.()}
	</button>
{/if}